Production of artificial tooth structures



- Dec. 10, 1946. J. G. DAY

PRODUCTION OF ARTIFICIAL TOOTH S TRUCTURES Filed Fe'b. 9; 1944 2 Sheets-Sheet N u 9/ x/x INVENTOR. v ,Jose /2 G/en Day v ATTORNEYS Dec. 10, 1946. J A'Y 2,412,207

PRODUCTION OF ARTIFICIAL TOOTH STRUCTURES Filed Feb. 9, 1944 2 Sheets-Sheet 2 INVENTOR. Joseph 6/9/7 Day ATTORNEYS Patented Dec. 10, 1946 PRODUCTION OF ARTIFICIAL TOTH STRUCTURES Joseph Glen Day, Toledo, Ohio, assignor, by

mesne assignments, to Dental Research Corporation, Chicago, Ill., a corporation of Illinois Application February 9, 1944, Serial No. 521,'707

The invention relates to the production of artificial porcelain tooth structures of predetermined shades.

Wearers of dentures demand that the portions of the denture which form the teeth provide the same appearance as natural teeth, particularly in the case of the portions of the denture which. form the front teeth. Therefore, it is necessary to exercise extreme care in the manufacture of porcelain tooth portions for dentures in order to secure the appearance of natural teeth.

` A person Who acquires a denture usually demands that theartificial teeth be of the same shade as the natural teeth that are replaced by the denture, so that as little as possible change in facial appearance is produced. Thus, it is necessary for a dentist to procure teeth of different shades for different patients.

In order that artificial teeth may have a natural appearance, it is necessary that the tip or ncisal section of each tooth be of a lighter and preferably more translucent porcelain than the remainder of the tooth. The necessity that the incisal section be of a lighter shade introduces another difficulty in the manufacture of porcelain teeth. In order that the tooth may have a natural appearance, the lighter shade of the incisal section must blend gradually with the remainder of the tooth so that there is no sharp line of demarkation between the shades.

It is necessary not only to have an even blending of the lighter shade of the tip with the darker shade of the remainder of the tooth, but also to have exactly the proper shade in every tooth in a denture, Any departure from the shade desired Would cause the set of teeth to be rejected by a dentist.

Artificial porcelain tooth structures have been manufactured in considerable quantities for several years. The methods by which such structures have been produced have been laborious because of the necessity of controlling the shades for the reasons stated above, and it often has been necessary to discard as much as twenty-five per cent of each lot produced by such methods because of irregularities in shade. Porcelain teeth produced by the methods heretofore in use have been quite expensive, and because of inadequacy of such' methods there exists a great unsatised demand for porcelain teeth of correct shade.

The principalobjeet ofthe invention is to pro Vide an apparatus producing porcelain tooth structures in'which the control of shadesis sub- -stantially infallible so as to e1iminate Waste.

More specific objects and advantages are appar nt 1 Claim. (CL 259- 57) from the description,` in which reference is had to the accompanying drawings illustrating apparatus suitable for use in the practice of the invention.

Figure I of the drawings is a perspective View of a mold of a conventional type which may be used, in the practice of the present method, to receive slurries of porcelain particles i or casting biscuits to be fired for producin porcelain tooth structures.

'Figure II is a transverse vertical section on the line II-II of Fgure I. i Figura III is a side elevation of a porcelain insert to be imbedded in a denture to form 'a tooth portion of the denture, which has been cast in the mold of Figure I.

Figure IV is a. rear elevation of the porcelain insert. v Figure V is a longitudinal vertical section of an apparatus for use in the practice of the invention. Figure VI is a plan View of the apparatus with one of the slurry containers removed. I Figure VII is a transverse vertical section taken on the line VII-VII of Figure V. i

These 'specific drawings and the specific description that follows merely disclose and illustrate the'invention and are not intended to impose limitations upon the claims.

In order to form a porcelain tooth portion of a predetermined shade, it is necessary-to cast 'the tooth portion from 'a slurry of porcelain particles of the proper composition to produce the desired shade. The porcelain for such a slurry is prepared by mixing porcelain particles'of different shades in proper proportions.

One of the most serious difiiculties in the 'meth'ods used during past years for the production of porcelain tooth structures has been theextreme-difficulty of maintaining a slurry of porcelain particles in a smooth uniiorm condition long enough to permit the introduction of the slurry into a mold, and preventin g segregation of par.- ticles of different shades. The porcelain particles of different shades have different specific gravities. Thus as soon as aslurry of porcelain particles is formed, the heavier particles immediatelybegin to collect in the form of a sediment in the bottom of the receptacle. tis Very difficult to prevent the formation of such *a sediment and to keep the porcelain particles of different shades uniformly distributed 'With respect to one another... I If the-porcelain particles of different shades are' not distributed uniformly *with respect to one another, it is impossibletowithdraw a part of. the slurry that will produce a porcelain tooth portion of the proper shade. If some slurry for casting a tooth portion is withdrawn from the upper part of the receptacle, the resulting tooth portion will be of one shade, and if some slurry for casting a tooth portion is withdrawn from the lower part of the receptacle, the resulting tooth portion 'will be of another ;shade Because of the rapidity with w-hich segre'gation of the poreclain particles of diiferent shades takes place in a slurry, it is difcult to mix' up a batch of any substantial size soas to produce -even momentarily a uniform slurry. Therefore, it has been the practice during past years to prepare at one time only a sufiicient amount of slurry for one tooth portion.

In order to prepare successive amounts of slurry, each of which is suflicient for one tooth portion, it has been the practice heretofore to place a mixture of dry porcelain particles of the proper composition in a small cup and to add an ;excess of distilled water. The cup is then placed upon a 'vibrating table where it is allowed to stand for 45 minutes. Durin this period the poreclain particles of various densities become thoroughly stratified. At 'the end of 'the period of vibration, the supernatant water 'is poured off, 'leaving the poi'celain particles 'in the form of a solid cake 'in the bottom of the .cup. In this cake the d'ensest partlcles are at the bottomand the density of the particles decreases uniformly from the bottom to the top of the cake. A sample of porcelain particles .in suffi cient amount for one tooth portion can 'be removed from the cake by cutting vertically through the cake so as to 'separate the same proportions of the heaviest partices at the bottom, the lightest 'particles at the top and the particles of intermediate density at various other levels in the cake. A sample 'thus separated from the cake can be mixed with a small amount of distilled water to produce a porcelain slurry in sufcient amount for one tooth portion, which is then transferred to the mold.

The preparation of a separate slurry'fo' each tooth portion is time consuming but has been considered necessary heretofore !because of 'the difiiculty of securing a uniform `distribution of the porcelain particles of different color in any larger amount of slurry. Even in the 'method heretofore used the shade of the tooth often is incorrect and a considerable amount of waste is caused by the discarding of teeth on account of incorrect shade. The small amount of slurry used in making one tooth portion is difilcult `'to handle, and lumping of the porcelain or entrap ment of bubbles often occurs so as to produce defects in the product which result in additional waste. v

The present invention, which obviates the foregoing difficulties that have been experienced in the practice of the methods by which considerable quantities of porcelain tooth structures have been manufactured in past years, is based upon the discovery of a much more advantageous method in which a, relatively large quantity of a slurry is subjected to substantially continuous agitation during the' pouring of successive tooth portions, a small proportion of the slurry being withdrawn for each tooth .portion. In order to can-y out such continuous ag'itation, a power` .ormly distributed with *respect 'to one another,

*particles of different shades, casting successive tooth portions from the slurry by withdrawing 'a small proportion of the slurry for each tooth portion, and t g, during the casting of the successive tooth portions, agitation of the slurry that 'is -sutficiently continuous to prevent appreciable segregation of particles of different lshades.

One type of mold in which the biscuits may be cast is illustrated in Figures I and II. such a mold ordinarily is made of a flexible, resilient glatin 'composition lo or of another fiexible, resilient composition 'such as 'soft .rubber. .Fissures or cracks ll are provided in the .flexible composition o which can be opened byfiexing the mol'd 'so as .to .permit the remova'l of the cast biscuits. Leading into the cavity l'2 in which the tooth portion is formed is a narrow sprue passage l 3shaving a flared 'entrance 4.

The cavity l2 may be of such a shape as to form the tooth portion illustrated in Figures III and IV. On the back of such tooth portion is provided a 'vertical web 'l'5 and a lateral web 16. 'The sides of the Vertical web 5 'and the u'pper surfaces of the lateral web 'IS may be serra'ted as shown in the drawngs. 'The rear face of the tooth portion proper may be provided with additional serrations !1 which, 't'ogether with the serrations on the vertical and lateral webs, permit 'the tooth portion to be anchore'd securely 'in a denture so -as to resist the forces to which the tooth portion is sub- J'ected when the denture is in use.

A tooth :portion such as that shown in Figures III and IV should be produced from porcelain of -two o'r three different shades. The lightcst shade of pcrcelain is used for the tip or incisal portion and the dar-kest shade of porcelain is used for the opposite end or gingival portion. The tooth structure illustrated in Figures III and IV is shown divided into three superimposed sections consisting of a gingival section A, a middle section B and an incisal section C. Although the blending of the porcelain of one section with the difierent shade of porcelain in an adjoining section should be very gradual so that no denite line of demarkation is visible, the approximate boundaries of the three superimposed sections are indicated by dashed lines in Figures III and IV.

In the use' of a mold such' as that shown in Figure I, a slurry of porcelain particles of such a composition as to produce the proper shade for the incisal section is first introduced *into 'the mold cavity !2 to the approximate depth of the section C` in Figure III. During the introduction of the slurry the mold, which is relatively transparent, is in front of a source of light which permits the depth of the slurry in the cavity !2 to be observed. After the casting of 'the incisal por tion, a slurry of porcelain particles of acomposition such as to produce the proper shade for the middle section i's introduced to the approx imate depth of the section B in Figure III. The remainder of the mold cavity and the sprue passage !3 are then filled with a slurry of 'porcela'in particles which produces a gingival portion of the proper shade. 'The successive layers of the different slurries are intended to diiiuse into one another to a slight extent so as to produce a uniicrm gradation of shade from one section to the next. Only two portions of different shade may be employed instead of the three portions indicated in Figures III and IV.

After the mold cavities have been filled, th

mold is allowed to stand on a vibrating table' for 105 minutes during which the porcelain particles settle so as to produce a relatively firm biscuit, leaving the excess Water at the top. The excess water is then sponged ofi at the entrances of the sprue passages and the mold is allowed to stand on the vibrating table for a few additional minutes. Finally the finished biscuits are removed from the mold by fiexing the sides of the mold downward so as to open the fissures il. The sprue formed in each sprue passage [3 is then removed and the biscuits are fired in the usual `manner to p roduce the finished porcelain tooth portions.

The substantially continuous agitation that is employed in the practice of the present method may be carried out by means of any desired power agitator. Figures V, VI and VII of the drawings illustrate one convenient form of power agitator that may be used. In that device a base !8 carries a housing !9 within which is a driving motor 20. Secured to the front of the motor is a transmission 2| which through couplings 22 drives a pair of rubber covered rollers 23 which are journaled at their opposite ends in a hearing block 24 mounted on the base !8. A bracket 25 is mounted at one end upon the base !8 and at the other end upon the bearing block 2 and carries fixed spacers 25 and adjustable spacers 21. Con tainers 28 are longtudinally positioned by the spacers 25 and 21 and rest upon the rubber covered rollers 23, both of which rotate in the same direction.

A slurry of porcelain particles 29 in each container 28 is continuously agitated by the rotation of the containers which is produced by the rotation of the supporting rollers 23. Each container 28 is provided with a cap 30 having a gasket 3! to make a water-tight connection between the cap and the container. Each cap 30 has a narrow spout 32 through which the slurry can be Withdrawn in small quantities.

It has been discovered that when the agitation of the slurry is interrupted, as by removing the container 28 from the rotating rollers 23, the porcelain particles of various shades remain substantially uniformly distributed with respect to one another for about 15 seconds. It has been discovered also that by inverting the container 28 and touching the end of the spout 32 to the flared entrance M of each sprue passage !3 in turn, equal quantities of the slurry can be introduced into six or eight mold. cavities within such period of about 15 seconds. The container 28 is then replaced upon the rotating rollers 23 to continue the agitation of the slurry in preparation for the casting of additional tooth portions. If the agitation of the slurry is interrupted for more than about 15 seconds, lumps form and segregation of porcelain particles of different shades begins, so that any slurry withdrawn from the container after the agitation has been interrupted for more than 15 seconds may not be of the proper shade and is likely to contain lumps and bubbles which cause the cast tooth portion to be defective.

The present apparatus provides a tremendous improvement in speed, as compared with the apparatuses that have been used heretofore to produc large quantities of porcelain tooth portions. An amateur can cast a set of six biscuits in about 45 seconds by the present apparatus, using slurries of three different shades, whereas it takes an averag skilled operator about seven to {eight minutes to cast a similar set of biscuits by the apparatuses heretofore used.

The present apparatus insures regular timing in the pouring of the successivo .portions of slurry. The regular timing afiorded by the present apparatus makes it possible to avoid letting each layer of slurry stand too long in the mold cavity before the succeeding layer is added. If a layer is allowed to stand too long in the mold cavity, it settles to such an extent that proper diffusion between such layer and the succeeding superi-mposed layer does not occur. The result is a sharp line of demarkation between the two shades of porcelain in the two layers, which makes it necessary'to discard the finished tooth portion as defective.

The shades of tooth portions produced by the present apparatus are almost infallibly correct, and the formation of bubbles and lumps is avoided so that the present apparatus substantially eliminates the twenty-five per cent loss due to defects and incorrect shading that has been common in the apparatuses heretofore used in the manufactre of porcelain tooth portions.

The specific composition of the slurries used in the practice of the present method may be th same as the composition of the porcelain slurries used in rior methods. Reference is made to Patent No. 2,196,258, issued April 9, 1940, for a disclosure of slurries, molds and general procedure that may be used in the practice of the present method. A slurry prepared by mixing a dry powder with water as described in said patent is -preferred The proportion of Water used in making the slurry may vary, but in general is about 11 cc. of distilled water per ounce of the dry powder.

In the preparation of a mold such as that shown in Figure I for the casting of a set of teeth, it is customa-ry to wash the mold with soap and water, rinse and dry thoroughly. The interior of the mold is then moistened with a wetting agent. The excess of wetting agent is removed and the mold is then dried thoroughly to leave a uniform thin film of wetting agent on all interior sur-faces. The procedure for preparing the mold for use is the same as the foregoing procedure which is commonly used.

various embodiments of the invention may be devised to meet variou requirements.

Having described my invention, I claim:

In apparatus for charging a mold cavlty with a fluid mix of liquid and ground porcelain-like material. in combination, a pair of substantially parallel transversely spaced and generally horizontal rollers, a driving motor mounted in position adjacent one end of said pair of rollers and having driving connection with at least one of said rollers for r'otating same, a plurality of containers adapted to be supported in coaxial and endwis spaced relation on said rollers and to be rotated about a generally horizontal axis by contact with said rollers, each of said containers being adapted to contain a fluid mix of liquid and ground porcelain-like material and to set up and maintain the particles of porcelain-like material in a substantially complete and uniform state of sus-pension in the, lquid throughout the bodies 4 of the fluid mixes by agtatng and. freely intermingling and moving the ngredients about a generally horizontal axs by the rotation of said containers, pom-ing spouts on said containers for poiring the fluid mixes from said containers and into the mold cavities while the porcelan-lke particles are in a substantially complete state of suspension in the lquid contents of the fluid mlxes, a bracket supported in position extending "longitudinally beneath the space between said rollers; and spacers adjustably mounted on said bracket and extending for cooperation with the ends of said containers to assure proper relative positioxi ng of the containers.

JOSEPH GLEN DAY. 

